The present invention relates to the diagnostic imaging arts. It finds particular application in conjunction with image guided surgery based on magnetic resonance images and will be described with particular reference thereto. However, it is to be appreciated, that it is also applicable to other types of diagnostic imaging procedures, such as CT, nuclear cameras, and the like.
In image guided surgery, a volumetric image of a region of interest of a subject is generated. Based on the medical diagnostic image, a surgical procedure, typically a minimally invasive surgical procedure, is planned. For example, one might determine an optimal path, direction of approach, and depth for a biopsy needle such that the tip of the needle accurately and precisely reaches the tissue to be biopsied without passing through or dangerously close to critical or impenetrable tissues. Once the surgery is planned, the biopsy needle or other surgical instrument is positioned relative to the patient for insertion along the planned trajectory. Of course, the accuracy of the surgical procedure is no better than the accuracy with which the coordinate systems of the patient and the planning image have been aligned and the accuracy with which any variation in their sizes has been scaled.
Various techniques have been utilized to bring the coordinate systems of the patient and the images into coordination. For example, the minimally invasive surgical instrument is sometimes carried by an articulated arm with resolvers, which arm is mounted to the diagnostic imaging system. In this manner, the physical positions of the imaging region and the surgical instrument are mechanically constrained. For greater accuracy and to provide greater flexibility by not requiring permanent mechanical interconnection of the surgical system and the scanner, systems have been added for monitoring the actual position of the surgical instrument in real time. Such instruments typically include infrared lasers, video cameras, acoustic signal generators, radio frequency transmitters, and the like. These systems calculate the actual position of the surgical instrument, in surgical instrument space.
In order to bring the surgical instrument space into coordination with the diagnostic image space, fiducial markers are often employed. For example, three or more fiducial markers, i.e., markers which are both imageable by the diagnostic imaging system and viewable by the real time surgical instrument space monitoring system are attached to a patient prior to imaging. When the diagnostic images are processed, the fiducials appear in the resultant image. By placing a tip of the surgical instrument or other characteristic part of it to each fiducial, the position of the fiducials in both image space and surgical instrument space can be determined. Once determined, the coordinate system and scaling of image space and surgical instrument space can be coordinated. One drawback to this technique is the potential for operator error. First, the fiducials have physical size. When the characteristic part of the surgical instrument is touched to the fiducials, there is the potential for error due to both operator skill and the physical size of the fiducials.
For greater flexibility in the usage of the diagnostic imaging system, the surgical instrument and its real time position monitoring system may not be permanently mounted to the diagnostic scanner. Rather, such systems may be removably mounted to the diagnostic scanner or mounted on movable platforms which are positioned adjacent the diagnostic scanner for use and moved to a remote location or to another scanner when the diagnostic scanner is used for other purposes. Each time the surgical instrument and its monitoring system are positioned or repositioned relative to the scanner, it is advantageous to realign the coordinate systems. To this end, calibration phantoms have been devised which are imageable by the diagnostic imaging system. Such phantoms typically include fiducial-like structures which are imageable by the diagnostic imaging system. The fiducials are also positioned where they can be touched by the characteristic portion of the surgical instrument system. Of course, rather than actually touching each fiducial-like structure, the characteristic part of the surgical instrument system can touch another structure at a known offset from the fiducial-like structure. Once the position of the fiducial-like structures of the calibration phantom are known in both the surgical instrument space and in diagnostic image space, the two coordinate systems can again be coordinated. Again, the accuracy with which the coordinate systems is aligned is dependent upon the skill of the operator in positioning the characteristic point of the surgical instrument and the physical size of the fiducial-like structures.
The present invention contemplates a new and improved automated calibration system which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a method of coordinating coordinate systems of a diagnostic imaging apparatus and an image guided surgery system is provided. A phantom is positioned in an imaging volume of the diagnostic imaging apparatus. The phantom includes at least three elements which are imageable by the diagnostic imaging apparatus and at least three markers whose location is determinable by the image guided surgery system. The imageable elements are held in a fixed position relative to each other and to the markers in such a manner that there is an a priori relationship between the markers and the imageable elements. A diagnostic imaging procedure is conducted on the phantom to determine locations of the imageable elements in diagnostic image space. The markers are monitored to determine their locations in image guided surgery space. From the a priori relationship between the markers and the imageable elements of the phantom, either the locations of the imageable elements in image guided surgery space are determined from the determined locations of the markers or the locations of the markers in diagnostic image space are determined from the locations of the imageable elements of the phantom. The determined locations of either the imageable elements or the markers in image guided surgery space are compared with the determined locations of the same in diagnostic image space and a coordinate transform for transforming between the determined locations in image guided surgery and diagnostic image space is determined.
In accordance with another aspect of the present invention, a phantom for coordinating a diagnostic image coordinate system of diagnostic image coordinate space and an image guided surgery coordinate system of image guided surgery space is provided. The phantom includes at least three diagnostically imageable elements which are bound in a polymeric binder. At least three markers which are monitorable by the image guided surgery system are mounted on the polymeric binder.
In accordance with another aspect of the present invention, an apparatus for coordinating coordinate systems of a diagnostic imaging apparatus and an image guided surgery system is provided. The diagnostic imaging apparatus non-invasively analyzes structure in an imaging region and generates electrical signals indicative thereof. A phantom which has at least three elements which are imageable by the diagnostic imaging apparatus and at least three markers with an a priori known relationship with the imageable elements is positioned in the imaging region. Cameras view at least the markers and generate electrical signals indicative thereof. An image guided surgery processor determines locations of the markers from the electrical signals from the cameras. A processor determines the locations of the imageable elements in image guided surgery space from the locations of the markers. A projection processor projects the determined locations of the imageable elements in image guided surgery space along each of three mutually orthogonal axes. An image reconstruction processor reconstructs the electrical signals from the diagnostic imaging apparatus into diagnostic image representations and into projection images along each of three mutually orthogonal axes to generate projection images in diagnostic image space. A coordinate system alignment transform processor compares the locations of the imageable elements in the projections in image guided surgery space and the projections in diagnostic image space and determines a transform between diagnostic image and image guided surgery space therefrom. A transform processor transforms the diagnostic image representations from diagnostic image space into image guided surgery space for display on a monitor.
One advantage of the present invention is that it provides for an automatic, machine implemented coordination of coordinate systems.
Another advantage of the present invention is that it eliminates variations in results due to variations in operator skill levels.
Another advantage of the present invention is that it provides for one-click coordinate calibration.
Another advantage of the present invention resides in the automatic generation of error and accuracy determinations.
Still further advantages reside in increased accuracy, repeatability, reliability, and simplicity.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.